Current supply system



6 Sheets-Sheet 1 c. E. LoMAx rs1-A1.

CURRENT SUPPLY SYSTEM Filed Feb. 12, 1941 NVENTORS CLARENCE E1 LOMAX BY PIER BAKKER ATTORNEYS Sept. 28," 1943. c. E. LoMAx ETAL CURRENT SUPPLY SYSTEM e' sheets-sheet 2 Filed Feb. l2. 1941 INVENToRs CLARENCE E LoMAx BY PIE-R BAKKER .dfn-laag M M ATTORNEYS Sept. 28, 1943.

C. E. LoMAx ET AL CURRENT SUPPLY SYSTEM,

Filed Feb. l2, 1941 6 Sheets-Sheet 5 VENTORS CLARE cE E. LoMAX K PIER BAKKER ATTORNEYS Sept. 28, 1943. c. E. LoMAx Erm.

CURRENT SUlPPLY SYSTEM Filed Feb. 12, 1941 6 Sheets-Sheet 4 QQ@ @wm mmnzmm :512 9.

Sept. 28, 1943. c. E. LoMAx ETAL CURRENT SUPPLY SYSTEM Filed Feb. l2, 1941 6 Sheets-Sheet 5 I.\"JENTOR$ CLARENCE EA LOMAX PIER BAKKER BY 'ofm' M SIEHE (uw A .O. O...

c. E. LoMAx ETAL 2,330,501

CURRENT SUPPLY SYSTEM Filed Feb. l2, 1941 6 Sheets-Sheet 6 1% La, g, QM d @En 4 amo. mmamzmkz.

spt, 2s, 1943.

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[NX/ENT R CLARENCE E.LOOBAX PIER BAKKER BY ATTORNEYS UNITED STATES PATENT OFFICE CURRENT SUPPLY SYSTEM Clarence E. Loma-x, Oak Park, and Pier Bakker, Chicago, Ill., assignors to Automatic Electric Laboratoriesflnc., a corporation ot Delaware Application February 12, 1941, Serial No. 378,646

17 Claims. (Cl. 171-314) The present invention relates to current supply systems and, more particularly, to improvements in supply systems of the character utilized in automatic telephone exchanges to supply divide a system including a charge testing circuit of the vcharacter described, wherein a source of counter E. M. F. is provided which is automati- 'cally included in and excluded from one of the rect currentto thevarious relays, operating magtest circuits in accordance with predetermined nets andother control elements of the automatic changes in the system voltage.

switchgar. Current supply systems convention- It is another object of the invention to provide ally used in small unattended telephone instala system of the characterdescribed, wherein lations of this character commonly include a unit PrOViSiOIlS are made fOr altering the magnitude which functions to convert alternating current 1o 0f the charge delivered tothe system battery of commercial frequency into direct current of to conform to changes in the speCC gravity 0f the proper voltage, and a storage battery which Athe battery OCCasiOhed by seasOIlal Changes in is connected across the main bus conductors ofl the temperature 0f the battery.

the exchange and serves as an emergency sup- It ls another object of the invention to provide ply source in case of commercial power failure, in a battery Charging ysystem utilizing a Charger and also to supp1y current to the load during' of the thermionic type an arrangement for propeak trailic periods when the current demand teCtng the charger against damage due t0 high may exceed the current rating of the converter voltage surges impressed 1113011 the input Circuit unit. thereof.

It is an object of the present invention to pro 20 It is still another object of the invention to vide a current supply system of the character provide in a battery Charging system utilizing described which is arranged for oompieie supera charger of the thermionic type an arrangement vision from a remote point, operates to maintain for preventing llasbbaoks through the Charger the switchboard voltage within limits satisfactory during Periods When the Charger iS being 00nfor reliable operation of the switchgear and also neotod to and disconnected from the system functions to provide improved switchboard rebatteryliability when the commercial power source fails. In each of the three illustrated embOdimerlts of It is a further object of the invention to pro.. n the invention there is provided a system which vide a eurreni; supply system of the chai-acte!- de includes a battery and a charging or rectifying scribed, wherein the control of the charging unit of the constant current type. The rectifyequipmentl is accomplished in a positive and reii ing unit functions to deliver current to the switchable manner through the provision of Chai-ge ing equipment constituting the system load at all testing apparatus which is fully automatic in times when the load current is appreciable, and Chai-acier and is exoeedingiy simple in arrange the battery functions primarily as a reserve curinent, rent source that is utilized during peak load pey It is another object of the invention to pr0 riods and in case of commercial power failure. vide a current supply system of the character de In each embodiment of the invention the system scribed, wherein provisions are made for utilizing battery is of the typo Commonly used in telephone the saine charge testing equipment for interme exchanges and includestwenty-four cells having diate and high charge tests of the system battery. at least a 100 ampere hour rating- A battery 0f It is another objeoi; of the invention to provide this character, when provided in a small exchange an improved system of the character described having a 5 ampere busy hour load, fOr eXamDie, wherein the oherge testing Circuits are only per has, when loaded, a voltage 0i substantially 48 iodically completed and wherein provisions are Volts When fully Charged and the Charging equipmade for sustaining the operation of the charge mont is not ln operationl Under normal Conditesting equipmentl during periods of commercial tions the total exchange carrying time of the batpower failure, tery is about 48 hours, and even though the busy It is a further object of the invention to pro- DeriOd load is aPPreCiably lenger than that nor- Vide Charge testing apparatus of the chai-notoimally 'encountered in small exchanges, the sysjust described, which is substantially nen-respon- 5o tem voltage is held at a velue of 45 volts or more sive to sudden and momentary changes in the for a period in excess of 17 hours. This voltage load imposed on the system but is faithfully reis entirely satisfactory for satisfactory operation sponsive to sustained and substantial changes in 0f the automatie sWitChgear DrOVided in the eX- the system load. change. In order to permit full charging of the It is another object oi the invention to prosystem battery without an excessive rise inthe system voltage during the nal charging periods, a source of counter E. M. F. in the form of two counter cells is provided which is arranged to be serially included ln one side of the supply circuit between the batteryand the load. Automatic testing and switching apparatus is provided for switching the counter cells into and out of the current supply circuit and for starting and stopping the charging unit. This apparatus includes high and low voltage test relays which are periodically connected across the main current supply buses of the system.- As thus connected,

the low voltage test relay normally tests the voltage of the battery directly and controls the starting of the charging unit when the battery voltage drops to a predetermined value. With the charging unit operating, the high voltage test relay operates when the battery voltage attains a predetermined value and causes switching operations which result in the inclusion of the counter cells in the current supply circuit. With the system in this condition the high voltage test relay continues to test the system voltage which, in eiect, constitutes a reference voltage that is less than the battery voltage by a substantially fixed amount, i. e., the voltage drop across the counter cells. When the system voltage again rises to the value required for operation of the high voltage test relay, the charging unit is stopped. Thereafter, and when the voltage o f the battery is, due to the discharge thereof or to a heavy load imposed on the system, decreased to a value such that the low voltage test relay fails to operate, the counter cells are automatically excluded from the current supply circuit.

In accordance with another feature of the present invention a voltage dropping device in the form of a resistor or an additional' counter vcell to the arrangement of the equipment whereby the charging unit is protected against high voltage s'rges appearing on the input circuit thereof.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, to-

gether with further objects and advantages thereof,v will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figs. 1 and 1A whenlaid end to end in ythe order named illusis included in the high voltage test circuit. This device is normally short-circuited but provisions are made for opening the short-circuiting path to include the device in the test circuit, thereby to compensate for a change in the specific gravity of the battery occasioned by a seasonal change in the temperature thereof.

In one disclosed embodiment of the invention a constant voltage rectierof the thermionic or dry disk type is provided which is operativer to deliver current to the load and the battery at all times. A second normally inactive rectifier of the constant current type is also-provided. In this embodiment of the invention the counter cell control equipment is utilized to cut the counter cells into and out of the current supply circuit in accordance with changes in the system voltage, in substantially the same manner as in each of the other disclosed embodiments of the invention. Additional equipment controlled in accordance with the magnitude of thesystem load is provided for starting and stopping the constant current rectier. This additional equipment includes a timing device which functions to delay the completion of the constant current rectifier output circuit for an interval following the completion of the input circuit to this rectier. The

timing device also functions to delay the opening of the input circuit for an interval following the opening of the output circuit of the constant current rectifier during the operation of the control equipment to exclude this rectier from the current supply channel.

1=`urtherfeatures of the invention relate to the arrangement of the apparatus whereby the periodic testing of the system voltage is sustained during periods of commercial power failure and trate one embodiment of the invention, Figs. 2

and 3 when laid end to end in the order named illustrate another embodiment of the invention, and Figs. 4 and 5 when laid end to end in the order named illustrate a'third embodiment of the invention.

Referring now more particularly to Figs. 1 and 1A of thedrawings, the current supply system there illustrated may be provided in asmall unattended exchange located in a community of limited population, and including trunking facilities to a distant central oice which comprises an alarm or supervisory operators position 20. The community exchange may, for example, comprise switching facilities terminating two h'undred lines or less. These facilities preferably comprise nder-connector links of the wellknown Strowger type. In order to facilitate a description of the mode of operation of the illustrated current supply system, a portion of the switching equipment provided in the community exchange has been illustrated in diagrammatic form. This equipment includes a nderconnector link 25 and alarm sending equipment I5 which terminates an alarm trunk 26 'extending to the operators position 20 in the distant central oce. Through the equipment provided at this position the operator has access, over a trunk 21, to the automaticswitching equipment .of the community exchange.

Briey described, the illustrated current supply system comprises a constant current rectifier extend to the component control elements conunit in the form of a motor generator set I0, which' is arranged to deliver direct current to a load I0 and also functions to charge the system battery 3|). This rectifying unit preferably includes a generator Ib of the well-known compound wound type h'aving a slightly drooping voltage characteristic. The alternating current motor Illa of the unit is arranged to receive current from the current supply terminals I I which terminate opposite sides of a 110-volt alternating current feeder circuit. The storage battery 30 is normally connected across the system bus l conductors I2 and I3 from which branch circuits stituting the load 40. 'In accordance with well established telephone engineering practice the positive bus conductor I2 is connected to ground. It will be understood that the load 40 is comprised of a large number of relay and magnet to deliver current to the 'battery 30 and the load 40 in parallel, a source of counter E. M. F. in the forii of a pair of series connected counter cells 3|,`each having a voltage of approximately 2 volts, is provided. Still further to stabilize the system 'voltage during those periods when the system battery 30 is being subjected to an equalizing charge, two additional series connected counter cells 32 are provided which are normally short-circuited through the contacts of the manually operable switch |14.

For the purpose of controlling the starting and stopping of Athe charging unit I0, and the inclusion of the counter cells 3| in the current supply circuit, a, control circuit is provided. Briefly described, this circuit comprises an alarm relay Rl20, a switching relay Rl25, a release relay Rl30, a start charging relay Rl35, a'low voltage test relay RMO, a generator test relay RHS, a second switching relay RI 50, a high voltage test relay R I 55, a transfer relay RI 60 a counter switching relay R I 65 and a supervisory relay RI 10. The

control circuit also includes an equalizing charge control key |14 and atest circuit control key |13, which latter key is provided selectivelyA to include the resistor |11 in the high voltage test circuit.

For the purpose of controlling the circuit |00, an interrupter |05 of the cam-operated motordriven type is' provided. This device comprises a plurality of cams |06 to |I2.- inclusive, which are mounted for rotation on the same shaft, and are driven through a gearbox, not shown, by an alternating current motor |86. The driving motor |86 is normally energized from the alternating current feeder circuit extending to the terniinals but is arranged to be energized from the storage battery 30 through the inverter |61, in case the commercial current source fails. The inverter |81 may be of any desired commercial form, although preferably it is of the well-known mechanical type. The enumerated motor-driven camshave associated therewith contact springs H3 to IIS, inclusive, which are provided to perform the control operations described with particularity hereinafter. In order clearly to show the relative positions of the actuating lobes and depressions provided in the cams, the portions thereof in which these lobes and depressions are formed have been shown in straight line form. It will be understood that the interrupter |05 is thirty revolutions per hour. y

circuit is periodically completed over which the winding of the low voltage test relay RMI is bridged across the bus conductors I2 and I3. Thus each time the cam-follower portion IHA of the upper contact spring II'I drops into the Vdepression Illa of the cam Ill a test circuit is completed which extends from the positive conthat the low voltage test relay RI periodically operates and restores so long as the'systeln voltage exceeds a value of 46 volts. As current is delivered to the load 40 from the storage battery 30, however, the voltage of this battery continues to drop until a value slightly less than 46 volts ,is reached. This decrease in the voltage across the bus conductors I2 and I3 may also be precipitated by a sudden and sustained increase in the load current. In any case, when the voltage across the conductors I2 and I3 drops to a value slightly less vthan 46 volts, the relay RHI is, during the next low voltage test period, insuilciently energized to operate. 'During the` last half of this period the cam follower portion Illa of the upper contact spring IISv drops into the depression IIIa to complete the prepared operating circuit for the `start charging relay R|35. This circuit extends from the positive conductor I2 by way of the contacts |23, the contact springs II8, the contacts |4I, andY the winding of RI35 to the negative conductor I3. When thus energized the relay RI35 immediately operates and In considering the operation of the sytsem I` illustrated in Figs 1 and 1A of the drawings it may be assumed that the storage battery 30 is substantially lfully charged so thatthe voltage across the twenty-fourcells thereof is approximately 49.5 volts; the high voltage test relay RI is constructed to operate when energized by a voltage of 52 volts; the low voltage test relay R|40 is constructed to operate. on any voltage exceeding 46 volts, and that appreciable although not excessive load current is being drawn from the battery 30. With these conditions present in the system the rectifying unit I0 is inactive and the counter cells 3|,lare shortcircuited through the contacts |65 ofl the counter cell switching relay RI65. Accordingly the voltage across the terminals of the storage battery 30 is the same as the voltage across the main bus conductors I2 and I3. Since the interrupter |05 is continuously operated, a test closes its contacts |39 to complete an obvious circuit for energizing the switching relay RI25. At its contacts |38, the`relay R|35 opens a point in the operatingV and locking ,circuits for the transfer relay RI60. At its contacts |36, the relay R|35 opens one of the supervisory signaling circuits described with particularity hereinafter. At its contacts |31, the relay R|35 prepares another of the supervisory signaling circuits.

The switching relay RIZS, upon operating, locks up in a circuit including the bus conductors I2'and I3 andthe contacts |28, |32 and |23.

Thus the relay R|25 is prevented from releasing when the contacts IIS are subsequently disengaged by the cam III to cause the deenergization and release of the start charging relay Rl35. In operating, the switching relay R|25 closes its contacts |26 to complete an obvious circuit for delivering alternating current to the motor |011, whereby operation of the rectifier unit I0 is initiated. As the motor generator set comes up to speed, the voltage across the output vterminals of the self-excited generator |0b rises to a value suflicient to cause the operation of the marginal generator test relay RMS. In operating, the relay RJ45 closes its contacts |46 to complete a circuit including the contacts A|21 for energizing the switching relay RI50. The relay RI50, in operating, closes its contacts |5| to connect the output terminals of the generator |0b across the load 40 and the storage battery 30 in parallel. Thus the generator Ib is connected to deliver current to the load 40 and also to the battery 30, in the event the' load current does not exceed the constant current rating thereof. At its contacts |52, the relay RIEO completes an obvious path in shunt with the contact springs IIII. At its contacts |53, the relay -RIEO prepares a high voltage test circuit over which the winding of the high voltage test relay RIEE is periodically bridged across the bus conductors I2 and I3 by the interrupter |05.

After operation of the motor generator set IO is initiated in the manner just explained, the voltage across the conductors I2 and I3 will almost immediately rise to a value exceeding 46 volts. Accordingly the periodic operation of the low voltage test relay RISO, under the control of the interrupter IOE, is again initiated. This relay, in operating, prevents the operation of' the start charging relay RI35 but performs no other function at this time. I

As indicated above, the relay RIEO, in operating, prepares a test circuit over which the winding of the high voltage test relay RIEE is bridged across the bus conductors I2 and I3. This test circuit is periodically completed by the cam II2 during each interval when t-he cam-follower` portion IIEaof the upper contact spring I|9 is dropped into the depression ||2a, and extends from the positive conductor I2 by way of the contacts |23, the contact springs II9, the contacts |53, the contacts of the key |13 and the winding of RIEE to the negative bus conductor I3. So long as the voltage impressed across the winding of the relay RIEE over this circuit does not exceed 52 Volts this relay is insuiciently energized to operate. When, however, the battery 30 is sufficiently charged so that the voltage thereacross exceeds 52 volts, the marginal high Voltage test relay RIEE operates when energized in the above-traced test circuit. In op.- erating, the relay RIEE closes its contacts |56 to complete a circuitincluding the contacts |62 for energizing the counter cell switching relay RISE. The relay RISE now operates and closes its contacts :|61 to complete a path for shortcircuiting the transfer relay RISO, this path extending from the positive bus conductor I2 by way of the contacts |21, I3| and |38, the winding of RISO, and the contacts |61, |62 and |56 back to the conductor I2. This path is interrupted at t-he contacts IES in response to the release of the high voltage test relay RIEE at the end of the high voltage test period in progress. When the short-circuiting path just traced is interrupted the two relays RISO and RISE are energized in series over a circuit which extends from the positive bus conductor .I2 by way of the contacts |21, I3I and |38, the Winding of RISO,4

the contacts |61, and the winding of RISE to the negative bus conductor I3. The current traversing this circuit is sufficient to maintain the relay RISE operated and to -cause the operation of the transfer relay RISO. The transfer relay RISO, upon operating, closes its contacts ISI to prepare the operating circuit for the release relay RISO and opens its contacts |62 further to interrupt the above-traced operating circuit for the counter cell switching relay RISE.

In operating, the switching relay RISE valso opens its contacts ISS to interrupt the path normally short-circuiting the counter cells 3|. Thus the indicated counter cells are serially included in the connection between thev positive terminal ofthe battery 30 and the positive bus conductor I2, whereby the voltage across the b us conductors I2 and I3 is decreased to a value approximately 4 volts less than the voltage across the terminals of the storage battery 30.

In other words, the system voltage is lowered to a value of approximately 48 volts although the battery voltage is approximately 52 Volts.

Following the operation of the relays RISE and RISO the interrupter IOE continues'periodically to complete the previously traced high and low voltage test circuits. In this regard it will be noted that both of these circuits are connected across the bus conductors I2 and` I3 rather than across the terminals of the battery 30. Accordingly the voltage periodically impressed across the high and low voltage test relays RIEE and RMO is 4 volts less than the voltage across the terminals of the lbattery ASO. If, with the system in this condition, a heavy load is imposed upon the system due to the start of the peak trac period, for example, the voltage across the bus conductors I2 and I3 may be lowered to a value less than 46 volts, in which case the low voltage test relay RISO fails to'operateV when this test circuit is next completed. When this occurs, the start charging relay RI35 is energized and operates during the last half.

of the low voltage test period. In operating, the relay RI35 opens its contacts |38 to interrupt the previously traced series locking circ-uit for the two'relays-RISO and RISE, causing these relays immediately to restore. In releasing, the relay RISE opens its contacts |61 to prevent the recompletion of the series locking circuit when the start charging relay RI35 restores at the end of the low voltage test period in progress. At its contacts ISS, the relay RISE again shortcircuits the counter cells 3|, thereby to equalize the voltage across the bus conductors I2 and I3 and the voltage across the terminals of the battery 30. Thus the voltage across the bus conductors I2 and I3 is increased by approximately 4 Volts. From this point on, the testing operations continue in the manner explained above until vthe two relays RISO and RISE are again caused to operate due to an increase in the system voltage. This increase may be Aoccasioned by a lightening of the load imposed upon the system or by an increase in the charge of the and RIEE is again '4 volts less than the voltage across the terminals of the battery 30. Assuming that -the load conditions are maintained in a manner such that the battery voltage continues to rise due tothe increased charge of the battery, the system voltage rises accordingly until a point is reached where the voltage across the bus conductors I2 and I3 exceeds a value of 52 Volts. When this occurs theY high Voltage test relay RIEE operates during the next succeeding high voltage test period and closes its contacts I E6 to complete the prepared operat- I ing circuit. for the release relay RISO. This'circuit extends from the positive bus conductor I2 relays R|55 and R|3I at the end of the high voltage test period in progress. The relay RI3II, in operating, also opens its contacts E32 to interrupt the locking circuit for the switching relay R|25. I'he r'elay R|25 now restores and opens its contacts |28 further to interrupt its own locking circuit. At its contacts |21, the relay R|25 opens the operating circuit for the relay RISIL At its contacts |26, the relay R|25 interrupts the circuit for energizing the motor |a. Thus the operation of the motor generator set Il is arrested, The relay RI5I), upon restoring, opens its contacts |5| to interrupt the circuit for delivering current from the generator Ib to the load III and the battery 30 in parallel. At its contacts |52, the relay R|50 opens the path shunting the contact springs H4. At its contacts |53, the relay R.|50 interrupts the previously traced high voltage test circuit. Thus the system is restored to normal. It will be understood that the operations just described continue to occur in response to changes in the system voltage. l

It is well known that batteries cannot be constructed so that all cells receive the proper amount of charge during regular daily charging cycles when incorporated in an installation of the character under consideration. The most convenient method of building up the charge on laggings cells is that of giving the entire battery an equalizing or overcharge. The accepted method of accomplishingr this in telephone exchanges is to Yovercharge the exchange battery periodically, usually at intervals of approximately thirty days. If the equalizing charge is omitted from the system maintenance the exchange battery will become undercharged and cannot carry the desired load. Moreover, a short battery life will result. Conversely, if the daily charging cycles or oat voltage is suiliciently high to prevent certain of the battery cells from lagging, the battery as a whole will be constantly overcharged, resulting in a short life. In equalizing the cell charge of the usual telephone battery from a constant current charger, the voltage at which the charge may be stopped, with assurance that all cells are fully charged, ranges from 2.25 to 2.9 volts per cell, depending upon the charging rate, the temperature of the battery, and other factors.

In the arrangement illustrated the two seriesconnected counter cells 32 are provided in the connection between the positive terminal of the battery 3,0 and the positive busv conductor I2 for the purpose of permitting an equalizing charge to be impressed upon the battery 3|) without an undue rise in the system voltage. These counter cells are normally short-circuited through the contacts |11 of the key |14. When, however, it is desired to subject the battery to an equalizing charge a maintenance man operates the key |14, which is of the locking type, to its oil-normal position wherein the contacts |15 are engaged and the contacts |16 and |11 are respectively disengaged. At the contacts |11, the path short-circuiting the counter cells 32 is interrupted, whereby the counter E. M, F. of these cells is included in the connection between the battery terminals and the bus conductors |2 and I3. Thus the system voltage is dropped approximately 4 volts below the voltage of the battery 30. 4At the contacts |16 a point is opened in the previously traced operating circuit for the release relay RIBII, thereby to prevent the high voltage test relay R|55 from arresting the operation of the motor generator l0 when itis operated to indicate that the system voltage is above 52 volts. At the contacts |15 an alternative circuit is completed for energizing the switching relay R|25, this circuit extending from the positiveiconductor |2 by way of the contacts |23 and |15, and the winding of R|25 to the negative conductor I3. When thus energized the relay R|25 operates to initiate the operation of the motor generator set I0 in the manner previously explained. Thereafter, and when the voltage of the generator Illb builds up to a value slightly exceeding the voltage across the battery terminals, the generator test relay RJ45 and the switching relay R|5|1 are operated in the manner previously described. The latter relay, in operating, completes the high voltage test circuit including the winding of the relay R|55 and closes its contacts |5| to connect the generator output terminals to the terminals of the battery 30. Thus the equalizing charge is started. As indicated above, with the key |14 in its off-normal position the high voltage test relay R|55 may be operated to cause the operation of the two relays RI 6U and R|65 in the manner previously explained, but is prevented from completing the operating circuit for the release relay RIBD. It will also be noted that When the counter cell switching relay R|65 operates it opens its contacts |66 to interrupt the path shortcircuiting the ycounter cells 3| so that an additional counter E. M. F. of 4 volts is inserted in the connection between the positive terminal of the battery 3U and the positive bus conductor I2. Thus the system voltage is dropped approximately 8 volts below that of the battery 30. It will also be noted that following the operation of the two relays R| and RIS5, these two relays may be released under the control of the low voltage test relay RMO and the relay R|35 if the system voltage drops below 46 volts. Thus, the counter cells 3| are, during the equalizing charge period, automatically included in and excluded from the connection between the positive battery terminal and the busconductor I2 in response to predetermined changes in the system Voltage. The switching relays R|25 and R|5U and the generator test relay RHS, on the other hand, remain operateduntil the equalizing charge key |14 is manually restored to normal. Obviously, when this key is returned to its normal position, during a subsequent visit of the maintenance man to the exchange housing the equipment illustrated, the contacts |11 are engaged to complete the path for short-circuiting the counter cells 32. Thus the system voltage, i. e., that across the bus conductors I2 and I3, is increased by approximately 4 volts. At the contacts |15, the above-traced auxiliary operating circuit for the switching relay R|25 is opened, thus restoring the control of this relay to the release relay R|30. At its contacts |16, the previously mentioned operating cirl cuit for the release relay RI 3|) ispreprepared.

During the high voltage test period next sucto taper the equalizing charge.

In subjecting the battery 30 to an equalizing charge in the manner pointed out above, the charge is preferably started at about 12 M. of a working day. Based on traic studies, the charges should, when started at this time, more than Vcarry the load during the afternoon and evening of the same day. From about 10 P. M. until midnight the battery lwill receive a charge of from 33% to 66% of the constant current rating of the generator |b. From midnight until 6 A. M. of the following day `the battery will receive even more charging current. At about 6 A. M. the exchange load should start to increase, thus again reducing the charging rate eiectively If the maintenance man who starts the equalizing charge revisits the exchange to stop the charge at 8 A. M., for example, a lower charging rate will thus be utilized during the last two hours of the equalizing charge. This decrease in the rate of charge at the end of the equalizing charge tends to avoid an unduly high Abattery voltage at the end of the charge.

Telephone exchange batteries which are commercially available in the art are open to the criticism that when the temperature thereof is dropped to a low value it is necessary to charge the 'batteries to a higher voltage in order t0 maintain thecorrect specic gravity thereof. In small unattended exchanges this is a decided disadvantage since usually the exchange building in which the equipment is housed constitutes an unheated enclosure which is subject to seasonal temperature changes. Accordingly, it is desirable in installati'onspf this type to provide facilities for changing the charge cut-off voltage to compensate for seasonal changes in the temperature of the battery. It is to this end that the resistor |11 is provided which may be included in the test circuitover which the high voltage test relay isl periodically bridged across the bus conductors I2 and I3. In the operation of the system this resistor is short-circuited through the contacts of the key |13 during the summer months when the temperature of the battery is substantially normal. During the winter months, however, the key |13 is maintained in its off-normal position, wherein the contacts thereof are disengaged serially to include the resistor |11 in the high voltage test circuit. As a consequence, a'

highervoltage between the bus conductors l2 and |3"is required to cause the operation of the high voltage test relay RI 55. Hence the battery voltage at which each charging operation is arrested R|55 `is increased, as will be clearly apparent from the preceding explanation.l The magnitude of this increase in the charge cut-off voltage is,

. of course, dependent upon the resistance value of the resistor |11. Ii' the value of this resistor is properly chosen, a charge cut-off voltage may be obtained which is correctly related tothe average seasonal drop in temperature of the particular location in which the battery 30 is installed.

tacts.

seized, the usual dial tone signal is transmitted therefrom over the trunk 21 to the headset of the operator attending the position 20 when the finder of thelink switches the calling trunk 21 .through to the connector portion of the link.

This statement is predicated on the assumption that the dial tone generator provided in the community exchange is operating properly. In this regard it will be appreciated that if the calling operator fails to hear the dial tone signal she is informed that the dial tone generating equipment or certain of the dial tone circuits are out of order. Upon receiving the dial tone signal the operator may cause the Wipers of the connector switch inthe link 25 to be positionedY on the test contacts |88 to |90, inclusive, by dialing the `directory number assigned to this contact set. After th'e test contacts are thus selected the usual line busy test operation occurs in the control equipment of the link. If the test contacts are idle, the usual switch-through operation Occurs in the link 25, whereby ground potential is 'impressed upon the private contact |90 and a.

circuit including the positive and negative line wipers of the connector switch and the winding of the supervisory relay R|10 is completed for ener` gizing the ring cut-off relay conventionally embodied in the connector portion of the link. When thus energized the ring cut-off relay operates to establish a signaling circuit which extends from the headset in use at the operators position 1 20 through the link 25 to the selected test con- Thesupervisory relay R|10 also operates when energized in this circuit and closes its contacts |1| to complete a circuit for transmitting signals through the link 25 'and over the trunk 21, indicative of the condition of the power and supervisory equipment provided in the commug under the control of the high voltage test relay In the normal operation and maintenance of A the system an operator attending the supervisory position 20 is assigned the duty of periodically just described. To this end, the operator attending the position 20 may seize one of the links provided in the distant community exchange.

that the under-connector link z5 is nity exchange.

The character ofthe signal transmitted to the supervisory operator depends upon a number of significant factors. Thus, iflthe current sup- .ply system illustrated is in its normal condition as described above and the busy tone generating equipment is operating properly, separate pulses of interrupted busy tone current are transmitted over the established signaling circuit. Under the conditions stated the path traversed by this current may be traced as extending from the ungrounded terminal of the `busy tone generator, not shown, by way of the busy tone lead |19, the

' contacts |36, the series-connected contact springs ||3, ||4,'A||5 and H6, the contacts |1|, the line contact |08, and the negative line wiper of the connector switch. From this point the busy tone current is transmitted through the llink 25vand over the trunk 21 to energize the receiver of the headset in use at the operators position 20. It will be noted that this branch of the signaling circuit is continuously and rapidly interrupted due to the separation of the contact springs ||3 under the control of the cam |06. It will also be noted that the above-traced branch of the signaling circuit is successively interrupted at the contact springs lll, ||5 and yI I6 due to the successive engagement of the projections |01a,

|08a and |0911 with the cam-*followerportions Ila, ||5a and ||6a, respectively. Qfthe upper contact springs III, |'I5 and H6. The latter interruptions in the signaling circuit constitute spacing intervals in the signal 'transmitted and each spacing interval is of significance in the operators translation of the signal. Thus it will be noted that a long uninterrupted signal is produced following the successive separation of the contacts IM, II and IIS. The operator is informed by counting the three spacing periods which follow the long uninterrupted signal that the current supply system is in normal condition and that the charging unit is not in operation. She is also informed by the tone of the signal, as derived from the busy tone generator, that this generator is operating. If at any time during the test period, the start charging relay RI 35 momentarily operatesto initiate the operation of the charging unit I0, in the manner previously explained, 'the contacts |36 are momentarily opened and the contacts |31 are momentarily closed, whereby the signaling current is, for a short interval, derived from the ringing current generator, not shown, over the lead |80 rather than from the busy tone generator. The reproduction of this splash of ringing current by the receiver provided at the operators position 20 serves to inform the operator that the ringing equipment is in proper working order.

It will be noted that if the start charging relay RI35 is operated and the two relays RMS and RI50 fail to operate a complete signal Vcomprising three spacing intervals is transmitted to the operator. Under normal conditions the generator test relay RI45 andthe switching relay RISO operate shortly following the operation of the start charging relay R|35. Accordingly if the three-spacing-period signal is reproduced by the receiver in use at thev operators position for a sustained period following the reproduction of the splash of ringing current, the operator is informed that a fault exists in the charging unit I0. On the other hand, if the switching relay RI50 operates in the manner explained above, it closes its contacts |52 to short-circuit the springs Ill. Accordingly, the separation of the contacts II4 by the cam projection I01a is ineffective to produce a spacing interval in the signal when the relay RI50 is operated. This, of course, means thatonly two spacing intervals are included in the signal transmitted to the operators position 20. Thus the operator is informed that the charging unit I0 is in operation, and that the voltage o f the battery is low. Moreover, if,the voltage of the battery remains low after operation of the charging unit I0 is initiated, the relay R| continues its periodic operation and functions to transmit a splash of 'ringing current over the signaling circuit during each long period separating the spacing lntervals. This recurrent ringing signal and the termination thereof whenthe battery voltage exceeds 46 volts, serves to inform the operator as to the charging interval required to remove the low voltage condition. When a signal is received indicating that the charging unit is operating, the operator may, by successive test calls at spaced intervals, ascertain whether or not the charging operation is completed Within a reasonable time interval. In this regard it will be understood that when the charging operation is completed the relays R|35 and R|50 are restored so that the normal busy tone signal vcomprising three spacing intervals is transmitted over the signaling circuit.

Provisions are made for transmitting an emergency alarm signal to the operators position 20, for example, in the event the alternating current source fails. Thus if the feeder circuit exotherwise deenerglzed, the normally energized alarm relay R|20 restores. In releasing, this relay closes its contacts |22 to shunt the contact springs lH5. At its contacts |23, the relay R|20 opens a point in the common portion of the operating, test and locking circuits for the relays R|25, RI35, R|40 and R|55. Thus any operated ones of the relays provided in the control circuit |00 are immediately deenergized and restore in response to the release of the alarm relay RI20. As a result, the current drain fromv the storage battery 30 is substantially reduced. At its contacts I2I, the relay R|20 completes a circuit for energizing the inverter |81. If this inverter is of the mechanical interrupter type, the start circuit therefor extends from the negative conductor I3 through the winding of the start relay embodied in the interrupter, and the contacts |2| to the positive conductor I2. When the start relay of the interrupter is thus energized, the interrupter operates to deliver alternating current to the motor |86, Whereby operation of the interrupter |05 is sustained. At its contacts |24, the relay RI20 completes an obvious path for impressing ground potential upon the alarm lead ISI. When this lead is grounded the alarm repeater operates in a wellknown manner to establish a calling circuit over the trunk 26. The completion of this circuit results in the energization ofa signal lamp provided .at the operators position 20. The operator, upon-observing the lighted condition of this lamp, is informed that a fault exists in the equipment provided at the distant community exchange. To determine the character of the fault she may route a test call to the test contacts |88, |89 and |90 in the manner just explained. In this case the signal which is transmitted to theoperators position 20 comprises only two spacing intervals which are separated by a relatively long interrupted busy tone signal. Thus with the contacts |22 engaged, the disengagement of the contact springs |I5 by the cam projection |08a is ineffective to produce a spacing period in the signal. Accordingly the two spacing periods produced by the successive separation of the contact springs II4 and IIS are relatively widely spaced. This Iwide separation between the two spacing periods serves to inform the operator at `the position 20 that alternating current power source has failed in the distant community exchange.

From the foregoing explanation it will be apparent that a wide variety of distinctive signals are transmitted to the supervisory operator's position 20 in an exceedingly simple manner with a minimum of equipment. It will also be understood that the operator upon receiving any signal indicating a fault in the distant community exchange may take the proper steps to see that the fault is corrected. Thus if a signal is received indicating that the feeder circuit extending to the terminals I l is deenergized, the operator may call the power company and request that the fault be corrected. If a signal is received indicating that certain of the equipment in the community exchange is not in proper working order the operator may dispatch a maintenance man to the exchange for the purpose of correcting the fault, and she may give rather detailed information as to the character of the fault.

Referring now more particularly to Figs. 2 and 3 of the drawings, the current supply system there illustrated' is essentially similar to that shown in Figs. l and 1A, with the excepbeen used to identify corresponding parts.

tion of the apparatus for controlling the charging unit and the switching of the counter cells. In order to indicate the similarity between the two systems the same reference numerals have In the arrangement illustrated in Figs. 2 and 3 an ladditional counter cell 33, normally short-circuited through the contacts of the switch 35|, is provided in lieu of the resistor |11 used in the system of Figs. 1 and 1A. The charging unit |a is preferably of the constant current thermionic or dry disk type. In this system a control circuit 200 is provided for starting and stopping the rectifier |011 and for controlling the' counter cell switching. Briefly con sidered, this control circuit comprises' a low voltage test relay R225, a locking relay R230, a pair of alarm relays R235 and R240, a switching relay R265,a start charging relay R245, a release relay R250, a stop charging relay R300, a high voltage test relay R3|0, a transfer relay R320, a control relay R330, and a counter cell switching relay R340. Three additional relays R220, R255 and R250 are provided which function to protect the rectifier |011 against damage dueY to high voltage surges impressed across the input terminals lla. For the purpose of controlling the alarm sending relay R235 to indicate a failure of the rectifier |0a, another relay R210 is provided which is bridged across a resistor 212 included in the connection extending from the positive output terminal of the rectifier |0a to the positive terminal of the storage battery 30a. The control circuit 200 also comprises an equalizing chargekey 345 which, in conjunction.with the knife switch 350, is utilized to condition the system for an equalizing charge of the storage battery 30a. All of the relays mentioned above are arranged to be controlled by a continuously operated motor driven interrupter |a of the cam-operated type which i's substantially similar in construction with the interrupter |05 provided in the system shown in Figs. 1 and 1A. In the system illustrated in Figs. 2 and 3, the inverter for energizing the driving motor of the interrupter |05a during periods of alternating current failure, the alarm sending equipment and the alarm signaling circuits have not been shown, but it will be understood from the above explanation how thesey features of the circuits illustrated in Figs. 1 and 1A of the drawings and described with particularity above may be incorporated in the system'of Figs. 2 and 3.

In considering the operation of the system lt tact springs 2|4 and the winding of R225 to the negative bus conductor |3a. So long as the system voltage, i. e., the voltage across the conductors |2a and |3a, exceeds 46 volts the low voltage test relay R225 operates each time the circuit just traced is completed. In operating, the relay R225-opens its `contacts 226 to interrupt the operating circuit for the start charging relay R245 and thus prevent the latter relay from operating during the last half of each low voltage test period. Immediately the voltage of the storage battery 30a, drops below a value of 46 volts, the low voltage test relay R225 fails to operate during the next succeeding low voltage test period. `During the last half of this test period thev cam-follower portion 2|5a ofthe upper contact spring 2|5 drops intothe depression 209a to complete the prepared operating circuit for the start charging relay R245. This circuit extends from the positive conductor |2a by way of the engaged contact springs 2| 5, the contacts 226 and the winding of R245 to the negative conductor |3a. When thus energized V the relay R245 operates and closes its contacts 246 to prepare a path for impressing ground potential upon the supervisory lead 213. At its contacts 241, the relay R245 prepares a locking circuit for itself. At its contacts 248, the relay R245 completes a circuit for energizing the relays R230 and R265 in parallel, this circuit extending from the positive conductor |2a by way of the contacts 248, 323 and and the parallel connected windings of the relays R230 and R265 to the negative conductor |3a. When thus energized the relay R230 operates and closes its contacts 232 and 233 to prepare the operating circuits for the alarm relays R235 and R240. At itA contacts 234, the relay R230 prepares the high voltage test circuit over which the relay R3|0 is periodically bridged across the bus conductors |2a. and |3a under the control of the cam-actuated springs 2| 8. At its contacts 23|, the relay R230 locks up in a circuit including the contacts and completes a locking circuit for the switching relay R265. The relay R265, upon operating, closes its conta-cts 266 to connect the input terminals of the rectifier |0a to the a1- may first be assumed that the rectier I0a is not supplied to the load afrom the battery 30a and the low voltage test relay R225 is energized and operates at two-minute intervals for low voltage test periods of ten second duration each, under the.control of the interrupter |0511. Thus Aduring each revolution of the cam 208 the camfollower portion 2|4a of the upper contact spring 2|4 drops'into the depression 200a so that the contact springs 2|4 are moved into engagement to bridge the relay R225 across the bus conductors I2a and |3a. 'I'his periodically completed low voltage test circuit extends from the positive bus conductor |2a b y way of the conternating current feeder circuit, and closes its contacts 261 to connect the output terminals of the rectifier to the terminals of the storage battery' 30a. Thus the charging operation is initiated.

During the revolution of the vcams 206 to 2| I, inclusive, which next succeeds the relay operations just described, the cam-follower portion 2|8a of the upper contact spring 2|8 drops into the depression 2| la, whereby the contact springs 2|1 are engaged to complete the prepared operating circuit for the alarm relay R240, this circuit extending from the positive conductor |2a by way of the contact springs 2|1, the contacts 233 and the winding of R240 to the negative conductor |3a. When thus energized the relay R240 operates and locks upin a circuit which extends from the positive conductor |2a by way of the contacts 325 and 243 and the winding of R240 to the negative conductor |3a. At its contacts 24|, the lrelay R240 prepares the above-mentioned path for impressing ground potential upon the supervisory lead 213. At its contacts 242, the relay R240 prepares a locking circuit for the start charging relay R245. Shortly following the operation of the alarm relay R240 the cam-follower portion 2| 4a of the upper` contact spring 2|4 again drops into the depression 2031;

to start another low voltage test period. In this regard it may be pointed out that immediately the rectifier |a is sarted the system voltage should rise to a value exceeding 46 volts. Accordingly the low voltage test relay R225 normally operates to open its contacts 226 and thus interrupt the operating circuit for the start charging relay R245 during the low voltage test period next succeeding the operation of the alarm relay R240. If, however, an extremely heavy load is imposed upon the system such that the system voltage fails to rise to a value above 46 volts during the interval which elapses between the operation of the relay R240 and the next low voltage test period, the relay R225 fails to operate at the beginning of this period a'nd accordingly the above-traced operating circuit for the start charging relay R245 is completed during the last half of the period. In operating,

the relay R245 closes its contacts to completethe prepared locking circuit for itself, this circuit extending from the positive conductor I 2a by way of the contacts 241, 242 and 226 and the winding of R245 to the negative conductor |3a.

y voltage ultimately rises to a value exceeding 46 volts the low voltage test relay R225 operates and` opens its contacts 226 to interrupt the above-traced locking circuit for the start charging relay R245. Accordingly the latter relay is 'caused to release and in so doing opens its contacts 241 further to interrupt itsown locking circuit. At its contacts 246, the relay R245 disconnects the supervisory lead 213 fromground, whereby the alarm signaling circuits are restored to normal, in which condition they are set to transmit a signal to a distant supervisory operators position indicating that the system voltage is normal. Atl its contacts 240, the relay R245, in releasing, interrupts the above-traced operating circuits for the two relays R230 and R265, but the latter relays are held operated over their locking circuits as traced above.

With the 'rectifier |0a in operation, charging current is passed through the battery 30a so that ultimately the voltage across the terminals of this battery, and hence the system voltage, will rise to a value exceeding 52 volts. When this occurs the high voltage test relay is sufliciently energized over the periodically completed high Voltage test circuit to operate. This test circuit may be traced as extending from the positive conductor |2a by way of the periodically engaged contact springs 2|0, the contacts 234 and the winding of R3|0 to the negative conductor |3a. In operating, the relay R3|0 closes its contacts 3|| to complete a circuit including the contacts 32| for energizing the control relay R330. The relay R330 now operates and closes its contacts 332 to complete a path for short-circuiting the lower winding of the transfer relay R320, this path extending from the positive conductor |2a by way of the contacts 3| I, 32| and 332, the lower winding of R320 and the contacts 252 back to the -positive conductor |2a. At the end of the high voltage test period in progress the contact springs 2|0 are disengaged to cause the deenergization and release of the high voltage test relay R320. This relay, upon restoring, opens its contacts 3| to interrupt the above-traced short-circuiting path and thus permit the lower winding of the relay R320 to-be energized in series with the winding of the relay R330 over a circuit which extends from the positive conductor |2a by way 10 of the contacts 252, the lower winding of R320, the contacts 332 and the winding of R330 to the negative conductor |3a. The current traversing this circuit is sullicient to maintain the relay R330 operated and to cause the operation of the transfer relay R320. In operating, the relay R320 opens its contacts 325 to interrupt the locking circuit for the relay R240 and thus cause the deenergization and release of the latter relay.

. At Vits contacts 32|, the relay R320 further interrupts the above-traced operating circuit for the relay R330 and the path for short-circuiting its own lower winding. At its contacts 322, the'relay )R320 prepares the operating circuit for the stop charging relay R300. At its contacts 323, the relay R320 opens a point in the above-traced operating circuits for the two relays R230 and R265.

. At its contacts 324, the re1ay'R320 prepares a circuit for energizing its own upper winding.

Asindicated above, the relay R330, in operating, closes its contacts 33| to complete the operating circuit for the counter cell switching relay 'R340. The relay R340, upon operating, opens its contacts 34| to interrupt the path short-'circuiting the counter cells 3|a and thus include these 35 cells in the connection between the positive terminal of the battery 30a and the positive bus conductor |2a. IThus the system voltage, i. e., that lmpressed upon the load and upon the high and low voltage test circuits, is decreased to a value substantially 4 volts less than the voltage across the terminals of the battery 30a. This decrease in the system voltage prevents the high voltage test relay R3|0 from operating during the high voltage test periods which immediately follow the relay operations just described. It will be understood, however, that since the system volt- Y age exceeds 48 volts even following the operation of the counter cell switching relay R340, the low voltage test relay R225 periodically operates 50 to prevent the operation of the start charging relay R245 during the last half of each low voltage test period. It will also be understood that thealarm relay R240 is energized for a short period during each revolution of the cam 2H. T he periodic operation of the latter relay is without eiect, however.

I f, following the operation of the counter cell switching relay R340 in the manner pointed out above,rthe peak traiic period of the day starts,

such that a sustained heavy load is imposed upon the system, the system voltage mafv drop to a value less than 46 volts. Accordingly the low voltage test relay R225 will fail to operate at the beginning of the low voltage test period which 35 first occurs after the drop in the system voltage.

As a result, the start charging relay R245 is energized and operates during the last halftof his test period. In operating, thei relay R245 closes its contacts 248 to complete the prepared circuit for energizing the upper winding of the relay R320 in parallel with the winding of the release relay R250. 'I'his circuit extends from the positive conductor 2a by way of the contacts 240 andV 324, and the parallel-connected windings of R320 and R250 to the 'negative conductor |3a.

When thus energized the relay R250 opens its contacts further to interrupt the operating circuits for the relays R230 and R265. At its contacts 252, the relay R250 interrupts the previously traced circuit for energizing the lower winding of R320 in series with the winding of the relay R330. When thus deenergized the relay R330 opens its contacts 332 further to interrupt the series circuit extending through its own winding and the lower winding of the relay R320. At its contacts 33|, the relay R330 opens the operating circuit l'or the relay R340. The relay R340 now restores and closes its contacts 34| to shortv is substantially above the normal system voltcircuit the counter cells 3|a, thus equalizing the v system voltage and the voltage of the storage battery a. Shortly following the release of the two relays R330 and R340 the cam-controlled l contact springs 2|5 are disengaged to cause the deenergization and release of the start charging relay R245. This relay, in restoring, opens its contacts 248 to interrupt the above-traced circuit for energizing the relay R250 in parallel with the upper winding of the relay R320. Thus the two relays R250 and R320 are caused to restore. From the above explanation it will be apparent that when a. heavy load is imposed upon the system at a time when the counter cells 3|a "are includedin the connection between the positive bus conductor I2a. and the positive terminal of the battery 30a, these counter cells are shortcircuited to increase the system voltage so that it equals the voltage across the battery 30a, and the operation of the rectifier |0a is not arrested. When the load imposed on the system is subsequently decreased, the system voltage will ultimately rise to a value exceeding 52 volts, whereby the high' voltage test relay R3|0 is again suiliciently energized to operate. When this occurs the three relays R330, R340 and R320 are caused to operate in the exact manner described above so that the counter cells 3|a are again included in the positive connection between the battery 30a, and the bus conductor l2a.

With the counter cells 3 la included in the positive connection between the battery 30a and the bus conductor |2a, and the rectier |0a in operation, the system voltage will ultimately rise to a value exceeding 52 volts. When this'occurs, the high voltage test relay R3|0 operates and closes its contacts 3|`| to complete the 'prepared circuit for energizing the stop charging relay R300, this circuit extending 4from the positive conductor |2a by way of the contacts 3| and 322, the winding of R300 and the contacts 341 to the negative conductor |3a. VWhen thus energized the relay R300 opens its contacts 30| to interrupt .the previously traced locking circuits for the two relays R230 and R265, causing both of these relays to restore. At the'end of the high voltage test period in progress, the relay R3|0 and the stop charging relay R300 are sequentially deenergized in an obvious manner. The relay R230, upon restoring, opens its contacts 23| further to interrupt the locking circuit for itself and the switching relay R265. At its contacts 232 and 233, the relay R230 opens the prepared operating circuits for the alarm relays R235 and R240. At its contacts 234, the relay R230 opens the high voltage test circuitto prevent further operation of. the relay R3l0. The switching relay R265, in releasing, opens its contacts 266 and 261 to interrupt the input and output circuits of the rectifier |0a. Thus the charging operation is arrested.

Tt will be noted that' the charging circuit is age. If an appreciable load current is delivered to the load 40a from the storage battery 30a after the charging circuit is opened, the voltage of the 'battery 30a quickly drops to its normal value which ranges from 48 to 50 volts. This, of course, means that during a low voltage test period occurring shortly after the charging circuit is opened, the low Voltage test relay R225 will fail to operate. Accordingly, the start charging relay R245 is energized and operates during thelast half of the low Voltage test period. In operating, the relay R245 completes the previously traced circuit for energizing the relay R250 in parallel with the upper winding of the relay R320, whereby the two relays R330 and R340 are caused sequentially to restore in the manner previously explained. `At the end of the low voltage test period, the three relays R245, R250 and R320 are caused to restore in the manner described above. Following the release of these relays the system is fully restored to normal. Y

The manner in which the battery 30a is subjected to an equalizing charge at regular intervals is substantially the same as described above with reference to the system illustrated in Figs. 1 and 1A. Thus when the equalizing charge control key 345 is operated to its oir-normal position, the contacts 341 are disengaged to open the operating circuit for the stop charging relay R300, and the contacts 346 are moved into engagement to complete an alternative circuit for energizing the two relays R230 and R265 in parallel. This alternative circuit extends from the positive conductor |2a by way of the contacts 30| and 346, and theparallel-connected windings of the relays R230 and R265 to the negative conductor |3a. When thus energized the two indicated relays both operate, assuming that they are not already in th'eir operated positions. In operating, the switch relay R265 closes the input and output circuits of the rectiie 1` V| 0a to complete the charging circuit and the locking relay R230 performs the functions described above. Concurrently with the operation of the key 345 to start the equalizing charge, the switch 350 is operated to open the path normally short-circuiting the counter cells 32a so that these counter cells are serially included in the positive connection between the battery 30a and the busA conductor |2a. 'The system voltage is accordingly dropped to a valuev substantially 4 volts less than the voltage of the battery 30a. Following the operation of the key 345 and the switch 350, the high and low voltage test relays and the counter cell switching relays are free to operate in the exact manner described above, the only diilerence being that with the contacts 341 disengaged the stop charging relay R300 cannot' be'energized in response to a subsequent operation of the` high voltage test relay R3|0. It will be understood, however, that when the key 345 is manually restored to normal to open the contacts 346 and close the contacts 341, the stop charg ing'relay R300 is immediately rendered operato cause the interruption of the charging circuit.

If this procedure is followed, the system voltage, i. e., that appearing across the bus conductors |2a and |3a, is prevented from rising to an unduly highvalue due to the highly charged condition of thefbattery. 30a. In this regard it will be understood that after the battery 30 has been subjected to a loadfor a short time interval the voltage thereof is rapidly 'reduced to normal, so

that the switch 350 may be closed to short-circuit the counter cells 32a without causing an objectionable rise inthe voltage across the bus conductors |2a and |3a.

As indicated previously, the counter cell 33, which is normally short-circuited through the contacts of the switch 35|, is providedy to change the high voltage charge cut-off point in accordance with variations in the characteristics of the battery 30a occasioned by seasonal changes in the temperature' thereof. More specically, the

counter cell 33 is s'hort-circuited through the contacts of .the switch' 35| during the summer months whenfthe temperature of the battery` 30a is relatively high and a relatively low charging voltage is suflicient fully to` charge the batv operation of the relay R220.

cam-follower portion 2|-2a of the upper contact` putv circuit of the rectifier |0a is in all cases interrupted substantially concurrently with the opening of the input circuit thereto in order to protect the rectiiier against flash-backs from the battery a. In operating, the relay R255 also closes its contacts 256 to prepare the operating circuit for the relay R220. .Assuming that the high voltage impressed across the terminals Ila continues for a reasonable time interval the camfollower portion 2|3a of the upper contact spring 2|3 drops into the depression 20`|a of the cam 201 so that the contact springs 2|3 are engaged to complete the prepared operating circuit for the relay R220. This circuit extends from the positive conductor |2a by way of the contacts 256, the contact springs 2 I3 and the winding of R220 to the negative conductor |3a. When thusenergized the relay R220 locks up in a circuitincluding the contacts 222 and 256 so that it remains operated aftersthe contact springs 2I3 are disv ,'for the relay R260. This circuit is completed ata the contact springs 2|2 shortly following the springs 2|2 drops into the depression 206a, the

` contact springs2|2 are engaged to energize the tery 30a. On the other hand, during the winter months when a high charging voltage is required to bring the specific'gravity of the battery 30a. upto normal during each charging operation, the switch is maintained in its open--circi'iitv position so that the counter cell 33 is serially in-- cluded in the positive connection between the battery 30a and the bus conductor I2q. It will be observed that with the countercell 33 included in this connection `the system voltage is at all times maintained at least 2 volts lower than the vvoltage of the battery 30a. This, of course,

means that the low voltage test relay R225 will operate at a higher battery voltage than with the counter cell 33' short-circuited and also that the operation of the rectiiier |0a will not be ter-A minated until the battery voltage is increased to a `value 2 volts higher than with the counter cell short-circuited. The use of the counter cell 33 in this manner also prevents the average system voltage from being higher during one season ofthe year, i. e., the winter months; than during the hot weather season of the year.

As indicated above, the three reiays R220, R255 and R260 constitute an automatic reclosrelay R260/.over a circuit which extends from the positiy'e conductor |2a by way of the contact springs-212,fthe contacts 22| and the winding of v.R260 tothe negative conductor |3a. In operating, the'relay R260 opens the path over which the winding of the marginal relay R255 is bridged across the input circuit supply terminalsv Ha. The relay R255 is thus deenergized and restores. -At its contactsl 256, the relay R255 opensy the operating and locking circuits for the relay R220 ing circuit breaker arrangement which functions minals I la. In explaining the operation of these relays it may be assumed thata high `voltage surge of short duration appears lacross the input terminals` llla at a time when the r ctifler |0a is in operation, so that therelay R2 5 is ener- 70 gized thereby. Immediately the high voltage surge occurs,the relay R255 operates and opens its contacts 251 and 258 to interrupt both the input and output circuits of the rectiiier |0a.

causing the latter relay to release. At its contacts 251 and 258, the relay R255 reprepares the input and output circuits of the rectiierV Ila. The relay R220, in releasing, opens the operating circuit for the relay R260. Theu relay R260 now restores to recomplete the input circuit of the rectifier |0a and to again bridge the winding oi the relay LR255 across the current supply terminals 'I la. If the high voltage surge across the terminals ||a expires during the period required for the relay operation just described, the three relays R255, R220 and R260 remain in their restored positions. If, on the other hand, the high voltage across the currentsupply terminals Ila still persists, the relay R255. immediately reoperates to perform the voperations described above. From this. point on the above described sequence of relay operations, involving the three relays R220, R255 and R260, is periodically repeated under the control of the interruptr |0511 until the high voltage condition is cleared. In this regard it will be apparent that the sequence oi these operations is such that the input side of the rectiiier |0a is only exposed to the high voltage for exceedingly short time intervals, insufficient to cause any damage to the rectier.

As indicated above, the relay R210, operating in conjunction with the alarm relay R235, func tions to control the alarm sending equipment,

not shown, in a manner such that4 an alarm is planation that during normal operation of the Inthis regard it maybe pointed out thattheoutrectifier to deliver current to the storage bat- Thus when the when the rectier |a is not in operation, the

operating circuit for the alarm relay R235 is held open at the contacts 232 of the restored locking relay R230. -If, however, the two relays R230 and R265 are operated so that the rectier |0a, is connected to deliver current to the storage battery 30a and the load 40a and no current traverses the connection between the output terminals of the rectifier and the terminals of the storage battery, the relay R210 remains in its restored position or releases, as the case may be, further to prepare the operating circuit for the alarm relay R235. If this condition prevails fora sustained time interval the operating circuit for the relay R235 is completed. More specifically, the circuit for energizing the relay R235 is completed when' the cam-follower portion 2|6a of the upper contact spring 2|6 drops into the depression 2|0a, this circuit extending from the positive conductor |2a by way of the contacts 21|, the contact springs 2|6, the contacts 232 and the lower winding of R235 to the negative conductor |3a. In operating, the v relay R235 prepares or completes a locking circuit for itself depending upon the position of the transfer relay R320. This circuit extends from' the positive conductor |2a by way of the contacts 325 and 231, and the upper winding'of tially less than the peak load demands of the system. A second constant current rectifier Ib is provided which is arranged to be switched into the current supply channel when the load current exceeds the -current rating of the rectifier 20, and to be switched out of the supply channel when the current demand drops to a value slightly less than the current rating of the rectifier 20. Preferably each of the two rectiers |0b and 20 is of the dry disk or thermionic type. The control of the constant current rectier |0b, the-control of the alarm circuits, and the control of the counter cell switching are effected through operation of a control circuit 400 which differs somewhat from the control circuits respectively included in the two embodiments of the invention considered above. Briefly described, this control circuit comprises a pair of switching relays -R4|0 and R430, an alarm relay R420, a pair of switching control relays R440 and R450, a, marginal current responsive relay R460, a controlA relay R410, a low voltage test relay R480, a release relay R520, a transfer relay R530, a high voltage test relay R540, a control relay R550 and a counter cell switching relay R560. These relays are arranged to be controlled by the cam-actuated contact springs 5|0 to 5|3, inclusive, embodied in the constantly operating Inotor-drlven interrupter |05b.

`In considering the operation of the system shown in Figs. 4 and 5, it may be assumed that the normal voltage of the system .battery is approximately 50 volts; th'e total load current R235 tothe negative conductor |3a. It will be y apparent, therefore, that if the relay R320 is operated, the circuit just traced is only prepared, whereas if the relay R320 is restored the circuit is completed. Assuming that the relay R235 is energized over its circuit, it remains in its operated, position wherein the contacts 236 are closed to impress ground potential upon the alarm lead 214. With this lead groundedfor a sustained time interval an alarm signal is transmitted to the distant supervisory operators position in the marmer explained above with reference to the alarm repeater forming a part of the system illustrated in Figs; 1 and'lA of the drawings. If the relay R320 is operated, the transmission of the alarm signal is delayed until the voltage of the battery a drops to normal to cause the release of the three relays R320, R330 and R340 in the manner explained above. During` this period the relay R235 is periodically energized for short timeintervals over its operating circuit as 'traced above and functionsx to impress ground pulses upon the alarm lead 214. These ground pulses are of insufficient duration to cause the transmission of an alarm signal to the distant supervisory operators position. It may occur that the fault responsible for the release of the relay R210 or the failure of this relay to operate will automatically be cleared before the-locking circuit for the alarm relay R235 is completed through the release of the transfer relay R320. Y In such case the relay R210 operates and opens its contacts 21| tg interrupt the Yoperatingcircuit for the alarm relay R235 and thus preventV further operation of the latter relay.

Referring nowmore particularlyfto Figs. V4 and 5 of the drawings, the system there illustrated comprises a storage battery 3017 which is normally oated across the output terminals of a constant voltage rectifier 20. This rectifierV has a full load current rating which is substanresistance are commercially available.

`rating of the system is from 5.5 to 6 amperes and that the rated full-load output current of the rectifier 20 is 3 amperes. ,It may also be assumed that the no-load voltage rating of the constant voltage rectifier 20 is approximately 51.5 volts. The low voltage test relay is adjusted to operate on any voltage above 48 volts and to fail to operate when energized with a voltage of lesser value, and the high voltage test relay R540 is arranged to operate on any voltage over 53 volts.l Under the conditions assumed the constant current rectier |01) should be adjusted'to deliver about '75% of the rated output current of the constant volt` age rectifier 20, i. e., a constant current of 2.25

amperes should be delivered from the rectifier I0b to the load 40h and the storage battery 30h in parallel, regardless of the load resistance, when this rectifier is connected in parallel with the constant voltage rectifier 20. Under` normal light-load conditions the constant current rectier |0b is disconnected from the current supply channel so that current is supplied to the battery 30h and the load 40h only from the constant volt-A age rectifier 20. With the system in this condition the continuously operated interrupter |0511 functions periodically to prepare the operating circuit for the slow-to-release switching-control relay R450. This circuit is only completed when the marginal current responsive relay R460 operates. Under theconditions assumed abovethe relay R460 should be constructed and 'adjusted to operate .when traversed by current of approximately 2.7 amperes and, having operated, to release only when the current flew therethrough` is decreased below a value of-approximately 0.2'

ampere. Marginal current responsive relays of this character having an exceedingly low winding Assuming that the load demands of the system exceed 2.7 amperes, the relay R460 operates and closes its contacts 46| to prepare the operating circuit for the relay R450. This circuit is thereafter completed when the cam-follower portion 5|2a of the upper contact springs 5|2 drops into the depression 50811 of the cam 508. More specifically, this circuit extends from the positive conductor |2b by way of the contact springs 5|2, the contacts 442 and 40| and the winding of R450 to the negative conductor |3b. This circuit is obviously opened at the contact springs 5| 2 when the cam-follower portion 5|2a of the upper contact springs SI2 is moved out of the depression 50311.. The relay R450, in operating, closes its contacts 45| to complete an obvious circuit for energizing the switching relay R4I0. At its contacts 452, the relay R450 momentarily short-circuits the relai7 R440 over a path which includes the contacts 442 andthe contact springs 5|2. 'I'his path is interrupted at the contact springs 5|2 when these springs are disengaged by the cam 508, permitting the two relays R440 and R450 to be energized 'in series over a circuit which includes the contacts 452 and 45|. 'Ihe current iiow over this series circuit is sumcient to maintain the relay R450 operated and to cause the operation of the relay R440. In operating, the relay R440 closes its contacts 44| to complete an obvious circuit for energizing the switching relay R430. It will be observed that an interval substantially equal to the period required for the cam 508 to close and then open the contact springs 5|2 separates the operation of the switching relay R4|0 and the operation of the switching relay R430. In this regard it will be noted that the relay R4|0, in operating, closes its contacts 4H to complete the input circuit for the constant current rectifier |01), and the relay R430, in operating, closes its contacts 43| to connect the output terminals of the rectiiier |b to the terminals of the storage battery 30h. The purpose of this arrangement is to insure complete operation of the rectifier |0b before a load is imposed thereon, whereby flashbacks through the rectifier are prevented, assuming this rectifier to be of the thermionic type. The relay R440, in operating, also opens its contacts 442 further to interrupt the above-traced operating circuit for the relay R450 and to prevent the short-circuiting of its own winding during subsequent operation of the interrupter |b periodically to close the contact springs 5|2.

Immediately the relay R430 operates, the maior portion of the load is shifted to the constant current rectifier |017.- Thus if the load current'is increased to a value of 3.5 amperes, 2.25 amperes of this load is assumed by the rectifier |0b and the remaining 1.25 amperes is supplied by the constant voltage rectier 20. As additional load is imposed upon the system, the increased load current is supplied by the constant voltage rectitier until a point isreached wherein both of the rectiers are supplying currents equal to their full-lord ratings. Any additional load current is supplied by the storage battery 3017.

The two rectiiiers I0b and 20 are operated in parahel until the load current supplied by these rectiers drops to a value below 2.45 amperes, at which time the current traversing the winding of the relay R460 is less than 0.2 ampere. When fr cccurs the relay R460 releases and opens its Iis 46| to deenergize the series-connected R440 and R450. The relay R440 immee the 1- -gs R430. The relay R430, upon g, opens s contacts 43| to interrupt the .between Stile output terminals of the recy restores and opens its cont-acts 44| to de-A tiiier |0b and the storage battery 30h. Shortly following the release of the relay R430, the relay R450 restores and opens its contacts 45| to deenergize the switching relay R4I0. At its contacts 452, the relay R450 further interrupts the series holding circuit for itself and the relay R440. The relayR4|0,in releasing, opens its contacts 4| to interrupt the input circuit of the rectifier |0b.

It will be observed that in this sequence of relayA or alarm signaling equipment to transmit a signal indicative of the low voltage condition. Thus during each rotation of the interrupter cams an obvious circuit through the contact springs 5H is completed for energizing the low voltage test relay R480. As long as the voltage exceeds 48 volts the relay R480 operates each time it is energized in this circuit and opens its contacts 48| 'to prevent the operation ofthe relay R410 during the last half of the low voltage test period. When, however, the system voltage drops to a value less than 48 volts, the relay R480 is insuiiiciently energized to operate. Accordingly, a cir.

cuit including the contacts 48| and the Contact springs 5|0 is completed for energizing the relay R410 during the last half of the low voltage test period in progress. When thus energized the relay R410 operates and closes its contacts 41| to complete a locking circuit for itself which extends from the positive conductor l2b by way of the contacts 533, 41| and 43|, and the winding of R410 to the negative conductor |317. The completion of this circuit prevents the relay R410 from releasing when the low voltage test period in progress is terminated through disengagement of the contact springs 5|0. At its contacts 412, the relay R410 completes a path including the contacts 532 for impressing ground potential upon the supervisory lead 415. When this lead is grounded the supervisoryv or alarm signaling equipment to which it extends is conditioned to transmit a signal indicative of the low voltage condition to a supervisory operators position located in a distant exchange, all in the manner described above with reference to the system shown in Figs. 1 and 1A of the drawings. If the low voltage condition should terminate, the relay R480 is again sudiciently energized to operate when the contact springs 5|| are closed by the cam 501. In operating this relay R480 opens its contacts 48| to interrupt the locking circuit for the relay R410'. The relay R410 accordingly releases and opens its contacts 412 to disconnect the supervisory lead 415 from ground. At its contacts 41|, the vrelay R410 further interrupts its own locking circuit.

In the event the constant voltage rectifier 20 should fail, the alarm relay R420 associated therewith is deenergized in a. well-known manner .understood inthe art. More specically, this `suliicient to cause the operation thereof.

deenergized and restores. In releasing, this relay closes yits contacts 42| to impress ground potential uponI the alarm lead 414. This lead extends to an alarm repeater of the character illustrated in Fig. 1 ofthe drawings, and when connected to ground causes the repeater to transmit an alarm to the distant supervisory operators position, all in the manner outlined above with reference to the alarm repeater forming a part of the system shown in Figs. 1 and 1A.

The counter cell switching control apparatus is used primarily during those periods when the battery 30h is being subjected to an equalizing l charge. In this regard it is noted that the constant voltage rectier 20 is, in accordance with well-known practice, equipped with a 'voltage control switch which, when operated, increases the output voltageof the rectifier from the normal value of 51.5 volts to a voltage of approximately 56 volts. Accordingly, when this switch is operated to start the equalizing charge, the system voltage is immediately increased to a value of 56 volts. When the cam 500 operates to permit engagement of the contact springs |3, following operation of the equalizing charge control switch embodied in the rectier 20, the vhigh voltage test relay R450 is energized by a voltage The circuit over whichthis relay is energized extends from the positive conductor |2b by way of the contact springs 5|3, the contacts 534 and the winding of R540 to the negative conductor |35.

In operating, the relay R540 closes its contacts 54| to complete an obvious circuit for energizing the relay R550. The relay R550 now operates and closes its contacts 55| to complete an obvious circuit for energizing the counter cell switching relay R560. At its contacts' 552, therelay R550 completes a path including the contacts 52| and 54| for short-circuiting the lower Winding of the transfer relay R530. This path is interrupted at the contacts 54| when the`high voltage test relay R540 restores at the end of the high voltage test period `in progress. When this path is opened, the lower winding of the relay R530 is energized in series with the winding of the relay the output voltage of this rectier to its normal value of 51.5 volts, the voltage across the bus conductors |2b and.' |3b is decreased accordingly, i. e., to avalue of 47.5 volts. Accordingly the low voltage test relay R480 will fail to operate and the relay R410 will operate shortly after the voltage control switch of the rectier 20 is restoredlto normal. In operating, the relay R410 closesits contacts 413 to complete the prepared circuit for energizing the release relay R520 in series with the upper winding of the relay R530. The relay R520 now operates and opens'its contacts 52| to deenergize the relay R550 and the lower winding of the relay 530. The relay 550 now restores and opens its contacts 552 further to interrupt the series locking circuit for itself and the relay R530. At its contacts 55|, the relay R550 interrupts the operating circuit for the counter cell Aswitching relay R560. Shortly following the release of the two relays R550 and R560 the low voltage test period in progress is terminated to cause the sequential release of the relays R410, R520 and R530, in a manner clearly apparent from the above explanation. The relay R560, in restoring, closes itscontacts 56| to again short-circuit the counter cells 3|b, whereby the full battery voltage is again impressed across the bus conductors |2b and |3b. Following the release of.

the relays R520 and R530 the voltage testing and counter cell switching equipment is fully restored to normal. It will be understood from the above explanation that in any case where the system R550 over a circuit which includes the contacts l 52| and 552. The current traversing'this circuit is sufficient to maintain the relay R550 operated and to cause the operation of the transfer relay R530. The relay R530, in operating, closes its contacts 53| to prepare a circuit for energizing its upper winding in seriesl with the release -relay R520. At its contacts 532, the relay R530 opens a point in the above-traced path for impressing ground potential upon the supervisory lead'415. At its contacts 533, the relay R530 opens a point in the above-traced locking circuit for the relay R410. At its contacts l534, the relay R530 opens the high voltage test circuit over which the relay R540 is periodically bridged across thebus conductors |2band |3b by the interrupter |055.

The relay R560, in operating, opens its contacts 56| to interrupt the path normally short-circuit' ing the counter cells 3| b. Thus the counter cells are serially included in the positive connection 11er 20 is manually restored to normal to decrease voltage rises to an unusually high value the sequence of relay operations just described will occur to cause the counter cells 3|b to b e serially included in the positive connection between the battery 30h and the bus conductor |212. It will also be understood that if the system voltage drops below 48 volts during an equalizing charge period, the relays R530, R550 and R560 will be released under the control of the low voltage test relay R480 and the relay R410 toexclude the counter cells 3|b from the positive connection a between the battery 30h and the conductor 12b,

whereby the system voltage and the battery voltage are equalized.

From the preceding explanation it will be noted that in each of the three disclosed embodiments of the invention, the high and'low voltage test circuits are, only periodically completed. The purpose o f this periodic testing arrangement is threefold. First, the periodic testing of the system voltage prevents the charging units from being prematurely started in response to sudden and momentary load surges which cause a momentary drop in the system voltage. Similarly, there is less likelihood of the high voltage test relays operating to cause premature counter cell switching or premature interruption of the charging circuits in response to momentary decreases in the load imposed on the system. The second advantage o f the periodic testing arrangement resides in the fact that these relays are not continuously subjected to voltage changes. Such continuousvoltage changes tend to alter the characteristics of the test relays and, more specifically, to' alter the voltage values at which these relays will operate and restore. With the arrangement illustrated, however, wherein the test relays are not continuously subjected to the system voltage but are only energized at widely spaced intervals of short duration, the alteration in the characteristics thereof is substantially minimized. Further, the periodic energization 

